One way to aseptically dispense a microbacterial sensitive fluid through a dispenser consists in storing the fluid in a bag-in-box (BIB) type container with a delivery tube comprising an aseptic one-way valve at the outlet of the tube. A type of aseptic valve consists of a so-called visco-elastic valve comprising a valve body presenting a cylinder or a truncated cone form and the valve body comprising an internal channel connected to one or several fluid delivery ports. The valve also comprises an elastomeric cylinder having an internal section smaller than the section of the valve body so that the elastomeric cylinder is tightly fitted over the fluid delivery ports and over the valve seat.
Such a valve is, for example, set forth in U.S. Pat. No. 7,243,682, U.S. Pat. No. 5,836,484 or WO 2006/063000. The dispensing is accomplished by the means of a pump that exerts a pressure on the flexible tube and on the fluid present in the tube, and then in the valve body internal channel and delivery ports. When the fluid pressure exceeds the pressure outside the valve, this pressure urges the elastic cylinder away from the valve body and the delivery ports. Fluid then flows out between the valve body and the elastic cylinder. When the pump is stopped, the pressure outside the valve body exceeds the fluid pressure and the elastic cylinder is clamped tightly against the valve body, thereby preventing flow back through the valve. Consequently flow is only permitted in one direction.
Yet, it has been observed in such dispensers that the aseptic state between two fluid deliveries is not maintained systemwide. Depending of the valve design, the visco-elastic valves can maintain a certain back-pressure after the pump has stopped and it can take a few minutes before the fluid pressure effectively drops to a lower pressure. Then at the exact closing of the valve the status of the valve is not certain as the valve is too close to an open position to ensure a full and firm closure.
Starting from a valve which is open and delivers a certain liquid flow, a reduction of the pressure of the liquid results in a reduced flow rate and further reduction of the pressure results in a situation where the flow rate reaches zero when the valve reaches what is called the closing pressure. At that point the check valve is in a not very stable status: it is close to being open yet is closed. This is represented by the valve typically slowly leaking a few drops of liquid thus possibly compromising the aseptic state of the remaining liquid. At that closing point, a typical valve, made with an elastomeric membrane fitted over a solid valve seat, the membrane is already fitted onto and in contact with the valve seat. However this fit is not very tight, as is demonstrated by the accumulation of a liquid droplet or dripping from the valve over a short time (up to one minute). After a minute or so of dripping, then the pressure in the delivery system upstream of the valve reaches another value where the valve is now holding a constant pressure over time called the holding pressure. During these phases the check valve is vulnerable to microbial contamination. This phenomenon has been particularly observed in situations where viscous fluids are dispensed or for fluids comprising particulates.